1. Field of the Invention
The present invention relates generally to an engine mounting arrangement and more specifically to an engine mounting arrangement which includes an elastomeric insulator including a chamber which may be hydraulically pressurized/depressurized in synchronism with the vibration of the engine despite the change in pressure transmission characteristics between the chambers which occur with engine change of engine vibration.
2. Description of the Prior Art
In a previously proposed dynamic spring constant reducing arrangement shown in FIG. 1 of the drawings, an elastomeric mounting insulator 1 having a hydraulic chamber 2 defined therein, is operatively interposed between an automotive engine 3 and the chassis 4. The hydraulic chamber 2 is fluidly communicated with an actuator arrangement 5 having a variable volume chamber 6 which is contracted and expanded in response to the rotation of a cam 7. The cam 7 in this instance is operatively connected to the crankshaft of the engine (not shown) so as to rotate in synchronism therewith. The operation of this arrangement is such that as the engine 3 vibrates in a manner to compress the insulator 1 and thus reduce the volume of the chamber 2 defined therein, the cam 7 is adapted to induce an expansion of the chamber 6 so as to relieve the pressure tending to develop in the chamber 2, and subsequently, as the engine moves away from the chassis 4 and the chamber 2 tends to expand, the cam 7 rotates to a position wherein the chamber 6 is contracted to maintain the pressure in the chamber 2 and prevent same from falling due to the expansion thereof.
With this type of arrangement the pressure transmitted from one chamber to the other assumes the form of a pressure wave which moves with a speed variable with the type of fluid involved, the dimensions of the conduit 8 interconnecting the chambers and the frequency with which the chambers are contracted and expanded (viz., engine vibration frequency), and thus requires a finite time to be transmitted from one chamber to the other. For example, in the case that the fluid used is water, through which a pressure wave propagates at 1800 m/sec., the insulator is used to support a four cylinder in line internal combustion engine and the chambers are interconnected by a conduit one meter long, when the engine is running at 1200 RPM and produces a vibration of 40 Hz the pressure wave produced has a wave length of 45 meters. Thus, because the wave must traverse a given distance (viz., the length of the interconnecting conduit) a phase lag of 8 degrees occurs between the chambers. However, when the speed of the engine is raised to 2400 RPM and vibrates at 80 Hz for example, the wave length of the pressure wave shortens to 22.5 m and the phase lag increases to 16 degrees.
Thus, with the above arrangement, it has been impossible to, over a wide range of engine operating conditions, achieve the desired suspension characteristics as a result of the change in time required for the pressure generated in one chamber to reach the other with change of vibration frequency and the inevitable asynchronization of the pressures therebetween.
A full and detailed disclosure of the above disclosed arrangement may be found in U.S. Pat. No. 4,154,206 issued on May 15, 1979 in the name of LeSalver et al.